Patch up the CRUSH map compatibility guards

The "ceph osd crush tunables optimal" and "ceph osd setcrushmap" commands left an incompatibility window. Close it by testing the proposed CRUSH change feature requirements against the existing cluster's feature bits.
Yeah, we don't compare directly with monitor options here, but we will report any down OSDs. I guess if we want to make this a leader-only function we could look at the Connections directly, but it's a lot less abstracted if we do that, and makes it harder to pull out into a utility system. ;)
But as it stands we tell them about old OSDs explicitly, and tell them "at least one of your 3 monitors is too old". That doesn't seem like too bad of a UI for admins to handle.